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XP19 Defrosting Unnecessarily

I have an Lennox XP19-060 HP connected to a G60UHV 135k gas furnace. It's about 28 degrees outside, so the system is running continuously, but maintaining temp fine. The XP19 is defrosting every 90 minutes on cue, but each time I go outside during defrost, there is no frost on any of the coils. I'm wasting gas during this time and the temp drops to about 70 degrees out of the vent during defrost from 90-95 which leaves a chill in the house. My question is, I thought the xp19 had demand defrost which didn't trigger unless frost was detected?

I have a Vision IAQ PRO and I have set it to run HP all the way down to 5 degrees with the gas locked out at 35 degrees and up. For me, it's not a question of whether the HP running (I prefer HP to run over gas, although gas is getting less expensive), but a question of why the demand defrost insists on defrosting every 90 minutes when there is no frost on coils.

the defrost t-stat does not know there is no frost on coil , it just senses temp which is below freezing @ 28 degrees , the clock in the defrost board is set to go in to defrost every 90 minuets if defrost t-stat is closed

Somethings not right with what you said when that thing goes into defrost you should be heating in gas. I believe with out making a phone call the furnace you mentioned has a heat rise somewhere around 30-50 degrees. Atleast thats about typical for most all furnaces. So at 70 degree supply temp your return air would be between 20 and 40 degrees. You must be freezing to death. I would look into that if i was you

I have the XP-16 which is demand defrost. I'm sure that the xp19 also is. There are three sensors that determine when to defrost. An ambient sensor, coil sensor and discharge line sensor. Based on their readings, determines when the unit goes into defrost, basically by measuring the amount of ice build-up. If 6 hours of run time has elapsed since the previous defrost while the coil temp remains below 35 deg., the unit will revert to time and initiate a defrost. The defrost board has diagnostic led's to let you know if the sensors are operating properly.

I have had problems on several occasions where the sensors had to be changed. As a matter of fact, I'm currently awaiting the new sensor harness as once again, it's not working properly. My current problem is that mine goes into defrost mode every 34 minutes whether it needs it or not. It only stays in defrost for several minutes, but with the frequency, it's annoying every time it activates since you feel the blast of cold air until the aux. heat strips kick on.

Yeah, I read the same thing in the XP19 installer's guide. I'm glad that I'm not the only one who is experiencing an anomaly. I have a tech coming out in a little while to investigate. Thanks for the help.

Edit Update: Tech came out and checked all sensors and they are all operating normally. Next, he checked the charge on the unit and that was normal. He suspects that it may be a bad board (board not maintaining memory and re-calibrating every 90 minutes). So, if it keeps happening they will come out and replace the board. Has anybody else had experience with this?

While I'm no tech, as I mentioned, there are leds that flash on the defrost board if there is a problem. One of the codes will indicate if the board is bad. I can only assume that based on the led's. he seems to think the sensors are ok. Based on my led's the system is working normally. While it's easy enough to change the sensor harness, they will do so to see if that helps my problem.

I will let you know the outcome once the harness is changed which should be some time next week.

Yeah, I read the same thing in the XP19 installer's guide. I'm glad that I'm not the only one who is experiencing an anomaly. I have a tech coming out in a little while to investigate. Thanks for the help.

Edit Update: Tech came out and checked all sensors and they are all operating normally. Next, he checked the charge on the unit and that was normal. He suspects that it may be a bad board (board not maintaining memory and re-calibrating every 90 minutes). So, if it keeps happening they will come out and replace the board. Has anybody else had experience with this?

Was your problem solved? I'm still having the same problem with mine as I stated above. It still goes into defrost every 34 minutes whether it needs to or not. I have a new thread that I started yesterday. I forgot about this old one.

Was your problem solved? I'm still having the same problem with mine as I stated above. It still goes into defrost every 34 minutes whether it needs to or not. I have a new thread that I started yesterday. I forgot about this old one.

I'll fix it for you. Send me a check for $500, and I promise by May, it won't be a problem anymore!